LED Blue Light-induced changes in phenolics and ethylene in citrus fruit: Implication in elicited resistance against Penicillium digitatum infection

- Light-emitting diodes blue light increases ethylene production in citrus fruits.
- Ethylene-related genes are differentially regulated by blue light.
- High blue light quantum flux levels increase the coumarin scoparone.
- Ethylene and phenylpropanoids are not key factors in blue light-induced resistance to P. digitatum.

The objective was to investigate whether LED Blue Light (LBL) induces changes in phenolics and ethylene production of sweet oranges, and whether they participate in LBL-elicited resistance against the most important postharvest pathogen (Penicillium digitatum) of citrus fruit. The expression of relevant genes of the phenylpropanoid and ethylene biosynthetic pathways during elicitation of resistance was also determined. Different LBL (wavelength 450 nm) quantum fluxes were used within the 60-630 μmol m−2 s−1 range. The HPLC analysis showed that the most relevant increase in phenylpropanoids occurred in scoparone, which markedly increased 3 days after exposing fruits to a very high quantum flux (630 μmol m−2 s−1) for 18 h. However, phenylpropanoids, including scoparone, were not critical factors in LBL-induced resistance. The genes involved in ethylene biosynthesis were differentially regulated by LBL. Ethylene is not involved in elicited resistance, although high LBL levels increased ethylene production in only 1 h.